Modern electronic devices are generally built with various components for implementing multiple functions, and such components include, for example, logic circuitries operating at a low voltage and driver circuitries operating at a relative higher voltage. Even for driver circuitries, voltages at different levels may be required. As such, voltage regulators are widely used in modern electronic devices to regulate a supply voltage and to provide an output voltage at a given level. By way of example, a voltage regulator may be integrated in a CMOS image sensor to give out predetermined voltages. According to the output voltage, voltage regulators are generally classified as positive voltage regulator and negative voltage regulator.
Conventional linear voltage regulators, however, can provide only a single voltage output range, i.e., either positive or negative. Specifically, the positive voltage regulator can output only a positive voltage, and the negative voltage regulator can output only a negative voltage. As a result, manufacturers in the electronic industry have to prepare many different kinds of voltage regulators, in order to meet the needs in different applications.
Conventional negative voltage drivers typically employ a negative charge pump and a regulator. The regulator usually consists of an operational amplifier, large power MOS devices, and a resistor divider. For designs with a single output voltage range, people have no special concern about the current leakage. However, when the semiconductor device gets miniaturized and the threshold voltage of the MOS devices is decreased, the current leakage becomes a serious problem that deteriorates the performance of the electronic devices.
Therefore, there exists not only a need for a voltage regulator providing a plurality of output ranges, but also a need for a voltage regulator that can reduce or prevent the current leakage. Advantageously, the present invention can meet at least one of the above needs.